There is a need for large-mass efficient support structures which interconvert between a reduced volume stowed condition and a deployed condition having sufficient axial, bending and torsional stiffness to support blanket arrays, such as blanket solar arrays on orbit, and for other applications.
As one example, NASA's Solar Array Structures Program has embarked on an effort to develop large-scale solar arrays having sufficient area to produce 300 kilowatts constant power. Solar arrays of this type must include a support frame having sufficient strength and stiffness not only to support a tensioned photovoltaic blanket array, but also having sufficient strength and stiffness compatible with orbit spacecraft maneuvers.
Conventional structural elements used in solar arrays and many other deployable structures have historically been either a rigid truss structure or Storable Tubular Extendible Members (STEMS). Conventional rigid truss structures can have better deployed properties relating to stiffness and buckling strength than conventional monocoque or slit-tube designs. However, both of these conventional structural elements have disadvantages.
The conventional and deployable rigid truss structure includes a copious number of longerons, battens and diagonals having numerous corresponding joints that individually and collectively can include substantial deadband (range of movement in which no action occurs) and therefore the structure may lack stiffness and precision. Additionally, trusses often stack sequentially bay by bay onto themselves which can result in a relatively large stowed volume. Sequential stacking also requires some method of sequencing the deployment of the truss structure. The high part count and precision assembly requirements make conventional deployable truss structures expensive.
STEMs by contrast can provide a relatively small rolled stowed volume as compared to the truss structure. The STEM structure can be deployed by extending the tip end of the structure from the rolled stowed volume. Forces stored in the structure in the rolled stowed volume can be sufficient for deployment of a STEM structure. However, STEMs typically deploy as a slit tube structure which may lack sufficient buckling capacity and torsional stiffness to act as a support in large structures. Because of the lack of buckling and torsional stiffness, STEM structures can be scale limited.
There would be advantages in a collapsible structure of efficient mass having sufficient axial, bending and torsional stiffness even during movement from the stowed condition to the deployed condition to support large solar arrays in orbit and during orbit maneuvers and in other applications which can be extensibly retractably deployed from a reduced volume stowed condition.